A control unit 13 moves an engine throttle 15 to the wide open position whenever the driver wishes to decelerate. This maximizes the transfer of rotational energy from the vehicle wheels 6 to a flywheel 12 which is coupled to a drivetrain 7,8,9 because pumping losses in the engine 2 are much reduced due to the open throttle. The energy stored in the flywheel 12 can be used at a later time to supplement the engine's motive power. The control unit 13 also controls an electro hydraulic clutch 11 which couples and decouples the flywheel to and from the drivetrain through a continuous variable transmission (CVT) 10. The gear ratio of the CVT 10 is set by the ECU 13.